Noise control of serrated trailing edge airfoil under small incidence angle
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摘要: 受猫头鹰寂静飞行能力的启发,锯齿尾缘设计被认为是一种有效的控制湍流边界层−尾缘干涉噪声的方法。本文采用隐式大涡模拟法,详细研究了嵌入式锯齿尾缘对NACA 0012翼型绕流的近场流动和噪声特性的影响,雷诺数为$9.6 \times {10^4}$,远场马赫数为0.1631,攻角为4°,计算采用的非结构化网格具有约7000万的自由度。在实际计算时,为促进流动快速转捩,在直尾缘和锯齿尾缘算例的翼型表面均布置了锯齿形粗糙元转捩带。研究结果表明:相比于0°攻角状态,${4^ \circ }$攻角下的噪声辐射增强,主辐射方向发生偏转,在该方向上锯齿尾缘实现了约2.5 dB的降噪,且在小攻角(4°)下,锯齿也会诱导出有利于降噪的侧边涡对结构。针对壁面压力脉动的分析表明:锯齿主要改变了尾缘附近的时空关联特性,且压力场不能直接由现有针对速度场的Taylor或椭圆近似模型定量描述;此外,锯齿在抑制尾缘噪声的同时,对翼型气动性能造成了一定损失。Abstract: Inspired by the silent flight capability of owls, the serrated trailing edge design is considered as an effective method to reduce the turbulent boundary layer-trailing edge interference noise. In this study, the near-field flow and noise characteristics of a NACA 0012 airfoil with additional serrated trailing edges are investigated in detail using an implicit large eddy simulation approach with Reynolds number Re = $9.6 \times {10^4}$, far-field Mach number Ma = 0.1631, and angle of attack $\alpha = {4^ \circ }$. The simulation adopts unstructured grids with 70 million degrees of freedom. In this particular calculation, a small sawtooth-shaped rough strip is added to the airfoil surface to facilitate the fast transition to turbulence for both straight and serrated trailing edge cases. At an angle of attack of 4°, an increase in noise radiation is observed with respect to that at an angle of attack of 0°, with a deflection of the primary radiation direction and a noise reduction of about 2.5 dB in this direction. The flow analysis shows that the sawtooth induces the regularly distributed vortex pair structures at its sides, which facilitates noise reduction in the far-field. The analysis of the wall pressure fluctuation shows that the sawtooth mainly changes the space-time correlation properties near the trailing edges, and the space-time correlation properties of the pressure cannot be described by the existing velocity-based Taylor or elliptical correlation models. In addition, the sawtooth suppresses the noise radiation while causing some loss to the aerodynamic performance of the airfoil.
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Key words:
- aeroacoustics /
- serrated trailing edges /
- noise control /
- compressible turbulence
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图 4 近场流动结构示意图。基于Q准则的等值面(Q = 1)识别的旋涡结构,以流向速度着色,背景为张量表征的噪声辐射
Figure 4. Schematic diagram of the near-field flow structure. The vortex structures are identified based on the Q criterion (Q = 1) and flooded by the flow velocity, with the background being the noise radiation characterized by the dilatation
表 1 计算参数设置
Table 1. The settings of computational parameters
算例 控制方式 攻角/$\left( ^\circ \right) $ 网格自由度 $\Delta {y^ + }$ h0 直尾缘 0 74501080 0.87 h6 锯齿尾缘 0 75903900 0.87 h0α4 直尾缘 4 74501080 0.87 h6α4 锯齿尾缘 4 75903900 0.87 表 2 气动特性对比
Table 2. Comparison of aerodynamic performance
算例 h0 h6 h0α4 h6α4 浸润面积S变化 — +6% — +6% 升力L变化 — — — +2.94% 阻力D变化 — +6.24% — +6.93% 升力系数${C_L}$变化 — — — −2.89% 阻力系数${C_D}$变化 — +0.23% — +0.87% 摩擦阻力占比 84.07% 85.29% 72.78% 74.40% 压差阻力占比 15.93% 14.71% 27.22% 25.60% -
[1] HOWE M S. Aerodynamic noise of a serrated trailing edge[J]. Journal of Fluids and Structures, 1991, 5(1): 33–45. doi: 10.1016/0889-9746(91)80010-B [2] LYU B, AZARPEYVAND M, SINAYOKO S. Prediction of noise from serrated trailing edges[J]. Journal of Fluid Mechanics, 2016, 793: 556–588. doi: 10.1017/jfm.2016.132 [3] AMIET R K. Noise due to turbulent flow past a trailing edge[J]. Journal of Sound and Vibration, 1976, 47(3): 387–393. doi: 10.1016/0022-460X(76)90948-2 [4] HUANG X. Theoretical model of acoustic scattering from a flat plate with serrations[J]. Journal of Fluid Mechanics, 2017, 819: 228–257. doi: 10.1017/jfm.2017.176 [5] AYTON L J. Analytic solution for aerodynamic noise generated by plates with spanwise-varying trailing edges[J]. Journal of Fluid Mechanics, 2018, 849: 448–466. doi: 10.1017/jfm.2018.431 [6] GRUBER M. Airfoil noise reduction by edge treatments[D]. Southampton: University of Southampton, 2012. [7] AVALLONE F, PRÖBSTING S, RAGNI D. Three-dimensional flow field over a trailing-edge serration and implications on broadband noise[J]. Physics of Fluids, 2016, 28(11): 117101. doi: 10.1063/1.4966633 [8] JONES L E, SANDBERG R D. Acoustic and hydrodynamic analysis of the flow around an aerofoil with trailing-edge serrations[J]. Journal of Fluid Mechanics, 2012, 706: 295–322. doi: 10.1017/jfm.2012.254 [9] AVALLONE F, VAN DER VELDEN W C P, RAGNI D, et al. Noise reduction mechanisms of sawtooth and combed-sawtooth trailing-edge serrations[J]. Journal of Fluid Mechanics, 2018, 848: 560–591. doi: 10.1017/jfm.2018.377 [10] TIAN H P, LYU B S. Prediction of broadband noise from rotating blade elements with serrated trailing edges[J]. Physics of Fluids, 2022, 34(8): 085109. doi: 10.1063/5.0094423 [11] WEI Y L, QIAN Y J, BIAN S Y, et al. Experimental study of the performance of a propeller with trailing-edge serrations[J]. Acoustics Australia, 2021, 49(2): 305–316. doi: 10.1007/s40857-021-00221-w [12] YANG Y N, WANG Y, LIU Y, et al. Noise reduction and aerodynamics of isolated multi-copter rotors with serrated trailing edges during forward flight[J]. Journal of Sound and Vibration, 2020, 489: 115688. doi: 10.1016/j.jsv.2020.115688 [13] QIAO W Y, JI L, TONG F, et al. Experimental and numerical study on noise reduction mechanisms of the linear cascade with serrated trailing edge[C]//Proc of the 20th AIAA/CEAS Aeroacoustics Conference. 2014: 3349. doi: 10.2514/6.2014-3349. [14] WANG L, LIU X M. Aeroacoustic investigation of asymmetric oblique trailing-edge serrations enlighted by owl wings[J]. Physics of Fluids, 2022, 34(1): 015113. doi: 10.1063/5.0076272 [15] ZHOU P, ZHONG S Y, LI X T, et al. Broadband trailing edge noise reduction through porous velvet-coated serrations[J]. Physics of Fluids, 2022, 34(5): 057112. doi: 10.1063/5.0089257 [16] HU Y S, WAN Z H, YE C C, et al. Noise reduction mechanisms for insert-type serrations of the NACA-0012 airfoil[J]. Journal of Fluid Mechanics, 2022, 941: A57. doi: 10.1017/jfm.2022.337 [17] HU Y S, ZHANG P J Y, WAN Z H, et al. Effects of trailing-edge serration shape on airfoil noise reduction with zero incidence angle[J]. Physics of Fluids, 2022, 34(10): 105108. doi: 10.1063/5.0108565 [18] WITHERDEN F D, FARRINGTON A M, VINCENT P E. PyFR: an open source framework for solving advection–diffusion type problems on streaming architectures using the flux reconstruction approach[J]. Computer Physics Communications, 2014, 185(11): 3028–3040. doi: 10.1016/j.cpc.2014.07.011 [19] ZHANG P J Y, WAN Z H, SUN D J. Space-time correlations of velocity in a Mach 0.9 turbulent round jet[J]. Physics of Fluids, 2019, 31(11): 115108. doi: 10.1063/1.5128424 [20] TAYLOR G I. The spectrum of turbulence[J]. Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences, 1938, 164(919): 476–490. doi: 10.1098/rspa.1938.0032 [21] HE G W, ZHANG J B. Elliptic model for space-time correlations in turbulent shear flows[J]. Physical Review E, Statistical, Nonlinear, and Soft Matter Physics, 2006, 73(5 Pt 2): 055303. doi: 10.1103/PhysRevE.73.055303 [22] CHOI H, MOIN P. On the space-time characteristics of wall-pressure fluctuations[J]. Physics of Fluids A: Fluid Dynamics, 1990, 2(8): 1450–1460. doi: 10.1063/1.857593